Hard disk for Music Server

I am building a PC as a Music Server.  Looking for help to pick hard disks.
Planning get 10 GB.

I am trying to get the best drives.....
Should I have say three 4 TB drives rather than one 10 TB?
How much capacity can one fill before it impacts performance? 70 %
Disk speed 5400 or 7200 rpm?
Brand of disk - HGST Ultrastar, WD Red, or WD Gold?

Thank you.
If you get 3 hard drives of 4G capacity, are you going to create a RAID 0 array to get your 10+G of space?
I worked for a hard drive manufacturer for many years and for music, it really doesn’t matter what type of drive you get. For music, you won’t see any difference in speed between 5300 or 7200 rpm. Actually, I even recommend against ssd for music. If you are using Roon or another app that has an index to your music, keep the index in memory or place that on ssd, that will give you better performance. If you build a RAID array or buy a single large disk, make sure you get a bigger disk to use as a backup
If you go with the  WD Red watch the model number. There was some recent controversy about the labeling and the storage method. See  https://arstechnica.com/gadgets/2020/06/western-digital-adds-red-plus-branding-for-non-smr-hard-drives/ 

Using 4 of the Red WD40EFRX 4TB in a RAID 5 configuration in my NAS with no issues. 
Raid 0 offers no backup, it only spans more than one drive into volume (s) Very bad if there is a drive failure. Raid 5 is good but difficult to repair if there is a failure. 1+0 is much better, gives you failure, hot swaps without downtime or data loss, but during the failure time you will suffer data SLOW downs big time, on a network sharing the files..

More smaller, faster, drives with STRIPPING, will blow your mind with speed. SSD RAID 1+0, 4-10, 2 gig SSD drives, Hot rod buddy...
FTH comes to mind, Faster than hell.

I ran SCSI II raid on my old Novel networks, for some manufacturing software...The 60 meg BOOT drive weighing close to 60 lbs each. Priam, drives with 10" platters? I think......OLD SCHOOL...LOL They were Raid 5 X 5s The rack was close to 400 lbs, the system 36, IBM ran on 220-240.  What a watt sucking setup....Sure was cool, though...HOT, was more like it, come to think of it.. Made barrels of all things...Paper, metal, HS, polys, overpacks....

Just curious about your need for 10 TB of storage - that's a lot!

Do you currently have a large collection already on hard drive that you are simply going to transfer? Or, do you have a CD collection that you are going to rip? If that latter, it it is going to take you a long time to rip 10 TB of CDs.

And, instead of ripping everything, you might think about combining a streaming service service and then ripping only those CDs that are not available from streaming. File the rest of your CDs away and just add them as needed and/or you find the time.

Of course, if you have something else going on that needs the 10 TB of storage (videos, photos, business, etc.) then ignore the above.
As someone who has a goodly amount of experience building my own very fast computers (which among other things I use for editing of 4K video material, which is a very challenging task for a computer), here are my thoughts:

I agree with @rbstehno that you don’t need speed. Also, given especially the need for a backup drive or drives I would choose a small number of large drives, rather than a multitude of smaller ones. And I don’t see any need for complicating things with RAID. Keep it simple!

What I would do is use a single 5400 rpm 10 TB drive for music storage, another 5400 rpm 10 TB (or larger) drive for backups, a self-powered external usb-connected 10 TB drive for a second backup, and something like a 7200 rpm 1 TB WD Gold drive as the system drive (i.e., the drive containing Windows and programs). (That’s more capacity than you’ll need for that drive, but I don’t think the Gold drives are available in smaller capacities). Or if you envision using the computer for unrelated purposes where a faster system drive may be desirable, consider a smaller SSD, perhaps even a Samsung M.2 2280 NVMe drive if your motherboard can support it, those being **extremely** fast.

To back up the music files I would periodically simply copy the files from the music storage drive to the other backup drives, telling Windows to skip files that are already there.

I would also consider using a disk imaging program to periodically create images of the system drive, storing the images on one or both of the backup drives. In the unlikely event of failure of the system drive that would avoid the necessity of having to reinstall and setup Windows and your programs. I suggest that you consider Terabyte Unlimited’s "Image for Windows" program, which I have used for many years with great results, or Acronis True Image, which seems to be fairly popular.

Finally, FWIW, my perception is that HGST drives (HGST now being a brand of WD) are not very popular these days, as evidenced in part by the limited number of reviews their recent drives seem to receive at NewEgg.com.

Good luck. Regards,
-- Al